I think that was more of a nod to the writer's and I assume director's respect for but disagreement with Ridley Scott's thesis. They don't actually think Decka

I think that was more of a nod to the writer's and I assume director's respect for but disagreement with Ridley Scott's thesis. They don't actually think Deckard is a replicant, but they're more than happy to channel the idea of him being a replicant, but it's through Gaff where it can either come across as subtle misdirection, a hint to a wayward soul (K), or just playing tricks on someone that presumably took over his job - "something in his eyes".